The present invention relates to incandescent lamps, and more particularly to lamps of the sealed-beam type which utilize a preformed reflector member.
Sealed beam lamps, particularly those of the type commonly used with motor vehicles, commonly comprise an envelope formed by a monolithic reflector member which is joined to a lens member to form an evelope enclosing one or more filaments. The reflector member is conventionally concave in form, its inner surface being generally parabolic. As is commonly known, when using a parabolic reflector it is advantageous to place the source of illumination as close to the focal point of the parabola as possible. Moreover when using two or more filaments, while it is obviously impossible to place both filaments at the focal point, it is still important that the filaments remain in the focal plane or latus rectum of the parabola.
Despite the fact that sealed beam lamps have been manufactured for decades and a great deal of effort has been expended in improving both their design and manufacturing techniques, the accurate placement of lamp filaments during the manufacture of the lamps has continued to be a problem. In particular, it has been found difficult to repeatedly and accurately place the lamp filaments in the desired relationship to the parabolic reflector curve preparatory to the permanent affixation of the filament and/or mounting members to the reflector body.
As will be recognized by those skilled in the art, sealed beam reflector members are commonly made of pressed glass, and formed by placing molten glass in a generally concave mold, then urging a ram having a formed, parabolic head into the mold to press the molten glass into the desired configuration.
When it is subsequently desired to place lamp filaments within the reflector, it is common to use a fixture in which the outer (convex) surface of the concave reflector member seats, then to bring a set of three alignment fingers into contact with the inner reflector surface. When the locating fingers have seated upon the reflector surface it is assumed that the mounting head carrying the fingers is in a desired relationship with the reflector surface. This relationship is relied up in supporting the lamp filaments at a predetermined position with respect to the fingers while the rigid filament mounting leads are permanently affixed to the filaments.
In theory, the foregoing procedure should provide a highly accurate, repeatable registration of the filaments with respect to the reflector surface. However, due to manufacturing tolerances and unforseen or irregular shrinkage or distortion of the reflector, or to a slight misregistration of the glass-pressing punch with respect to its cooperating mold, accurate location of the filament within the reflector is not consistently achieved.
In particular, a slight shift or misregistration of the punch with respect to the glass-pressing mold causes a commensurate shift of the reflector inner surface with respect to the fixture which receives the outer reflector surface during the filament mounting operation. In such a case, or in the event that the reflector member has been warped slightly during the cooling process, the locating fingers of the filament-mounting fixtures do not encounter the same areas of the reflector parabola in every instance. As a result, placement of the filament within the reflector member is irregular, causing the optical properties of the finished lamp assemblies to be irregular.
Accordingly, it will be appreciated that it would be highly desirable to provide means for accurately locating a filament within a sealed beam lamp reflector.
It is therefore an object of the present invention to provide an improved reflector susceptible of more accurate filament location than hereinbefore possible.
Another object of the present invention is to provide a parabolic reflector whose configuration allows a precise determination of predetermined points of the parabola.
Yet another object is to provide a generally parabolic reflector with locating means from which the latus rectum of the parabola may be inferred.